Composition comprising surface modified high index nanoparticles suitable for optical coupling layer

ABSTRACT

Presently described is a method for coupling an optical film to a substrate, laminated optical constructions comprising an optical film and an optical coupling layer disposed on a surface layer of the optical film, and coating compositions useful for optical an optical coupling layer. The coating compositions comprise at least 40 wt.-% inorganic nanoparticles having a refractive index of at least 1.85 and a polymeric silane surface treatment.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 14/350,416, filed Apr. 8, 2014, which is a national stagefiling under 35 U.S.C. 371 of PCT/US2013/025511, filed Feb. 11, 2013,which claims priority to U.S. Provisional Application No. 61/604,169,filed Feb. 28, 2012, the disclosures of which are incorporated herein byreference in its entirety.

BACKGROUND

Organic Light Emitting Diode (OLED) devices include a thin film ofelectroluminescent organic material sandwiched between a cathode and ananode, with one or both of these electrodes being a transparentconductor. When a voltage is applied across the device, electrons andholes are injected from their respective electrodes and recombine in theelectroluminescent organic material through the intermediate formationof emissive excitons.

In OLED devices, over 70% of the generated light is typically lost dueto processes within the device structure. The trapping of light at theinterfaces between the higher index organic and indium tin oxide (ITO)layers and the lower index substrate layers is the major cause of thispoor extraction efficiency. Only a relatively small amount of theemitted light emerges through the transparent electrode as “useful”light. The majority of the light undergoes internal reflections, whichresult in its being emitted from the edge of the device or trappedwithin the device and eventually being lost to absorption within thedevice after making repeated passes.

Various light extraction films have been described for use with OLEDdevices for the purpose of increasing the amount of useful light.Industry would find advantage in compositions suitable for couplinglight extraction films to OLED devices.

SUMMARY

In one embodiment, a method for coupling an optical film is describedcomprising: 1) providing an optical film; 2) providing a substrate; 3)applying an optical coupling layer to a surface layer of the opticalfilm, the substrate, or a combination thereof; wherein the opticalcoupling layer comprises at least 40 wt.-% inorganic nanoparticleshaving a refractive index of at least 1.85, and a polymeric silanesurface treatment; and 4) laminating the optical film to the substrateforming a laminated optical construction.

In other embodiments, laminated optical constructions are describedcomprising an optical film; an optical coupling layer disposed on asurface layer of the optical film. The optical coupling layer comprisesat least 40 wt.-% inorganic nanoparticles having a refractive index ofat least 1.85 and a polymeric silane surface treatment. A substrate isbonded to the optical coupling layer at an opposing surface to theoptical film. In some embodiments, the optical coupling layer of themethod and laminated optical construction is disposed on a surface layerof the optical film wherein the surface layer has a refractive index ofat least 1.60. In one embodiment, the laminated optical construction isan intermediate. In this embodiment, the substrate may be a releaseliner. This intermediate may then be provided to an OLED manufacturerthat removes the release liner and bonds the optical coupling layer toan optical substrate such as an organic light emitting diode (OLED)device.

In another embodiment, coating compositions are described comprising atleast 40 wt.-% inorganic nanoparticles having a refractive index of atleast 1.85 and a polymeric silane surface treatment. In one embodiment,the coating composition may consist entirely of the surface treatedinorganic nanoparticles, i.e. the coating composition may be free of(meth)acrylate monomers, particularly those having a molecular weight of1,000 g/mole or less.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated in and constitute a part ofthis specification and, together with the description, explain theadvantages and principles of the invention.

FIG. 1 is a diagram illustrating layers of a light extraction film;

FIG. 2 is a perspective diagram of one-dimensional periodic structures;

FIG. 3 is a perspective diagram of two-dimensional periodic structures;

FIG. 4A is a diagram illustrating a first multi-periodic zone ofnanostructures with different pitches;

FIG. 4B is a diagram illustrating a second multi-periodic zone ofnanostructures with different pitches;

FIG. 4C is a diagram illustrating a third multi-periodic zone ofnanostructures with different pitches;

FIG. 4D is a diagram illustrating a fourth multi-periodic zone ofnanostructures with different pitches;

FIG. 4E is a diagram illustrating a fifth multi-periodic zone ofnanostructures with different pitches;

FIG. 4F is a diagram illustrating a multi-periodic zone ofnanostructures with different aspect ratios

FIG. 4G is a diagram illustrating a multi-periodic zone ofnanostructures with different shapes;

FIG. 5 is a diagram of a light extraction film having nanoparticlesapplied in a sub-monolayer over periodic structures;

FIG. 6 is a diagram of a light extraction film having nanoparticlesdistributed throughout a backfill layer;

FIG. 7 is a diagram of a top emitting OLED display device with a lightextraction film;

FIG. 8 is a diagram illustrating laminating a light extraction film toan OLED device;

FIG. 9 is a diagram illustrating laminating a light extraction film toan OLED device.

As used herein “optical film” generally refers to a light transmissivefilm. Optical films are typically utilized in a manner wherein anoptical film is disposed between a light source and a viewer. Theoptical coupling layer described herein is particularly suitable to bedisposed upon a surface layer of an optical film having a refractiveindex of at least 1.60, such as the backfill layer of a light extractionfilm.

Light extraction films and uses of them for OLED devices are known.Light extraction film generally refers to film having extractionelements that enhance light extraction from self-emissive light sources.The extraction elements (also referred to as extraction features orextraction structures) are nanostructures or microstructures that canoptionally be periodic, quasi-periodic, random, or may comprise multiplezones with different periodic structures in each zone. For embodimentswhere the extraction elements are non-random structures, the extractionelements may be referred to as engineered structures, or engineerednanostructures. Examples of light extraction films are described in U.S.Patent Applications Publication Nos. 2009/0015757, 2009/0015142,2011/0262093 and in U.S. patent application Ser. No. 13/218,610,incorporated herein by reference.

Light extraction film typically includes a substantially transparent(flexible or rigid) substrate, extraction elements, and a planarizingbackfill layer. FIG. 1 is a diagram of the construction of a lightextraction film 710. Light extraction film 710 includes a substantiallytransparent substrate 712 (flexible or rigid), low index extractionelements 714, and a high index backfill layer 716 forming asubstantially planar surface over extraction elements 714. The term“substantially planar surface” means that the backfill layer planarizesthe underlying layer, although slight surface variations may be presentin the substantially planar surface.

The extraction elements for light extraction films can be formedintegrally with the substrate, or formed in a layer applied to thesubstrate as illustrated for example in FIGS. 1-3. For example, theextraction elements can be formed on the substrate by applying to thesubstrate a low-index material and subsequently patterning the material.The extraction elements may be nanostructures or microstructures.Nanostructures are structures having at least one dimension, such aswidth, less than 1 micron. Microstructures are structures having atleast one dimension, such as width, between 1 micron and 1 millimeter.The extraction elements for light extraction films can beone-dimensional (1D) periodic structures, meaning the extractionelements are periodic in only one dimension, that is, nearest-neighborfeatures are spaced equally in one direction along the surface, but notalong the orthogonal direction. In the case of 1D periodicnanostructures, the spacing between adjacent periodic features is lessthan 1 micron. One-dimensional structures include, for example,continuous or elongated prisms or ridges, or linear gratings. FIG. 2 isa perspective view illustrating one embodiment of 1D periodic structures32, in this example linear prisms, on a substrate 30.

The extraction elements for light extraction films, can also betwo-dimensional (2D) periodic structures, meaning the extractionelements are periodic in two dimensions, that is, nearest neighborfeatures are spaced periodically in two different directions along thesurface. In the case of 2D nanostructures, the spacing in bothdirections are less than 1 micron. Note that the spacing in the twodifferent directions may be different. Two-dimensional structuresinclude, for example, lenslets, pyramids, trapezoids, round or squareshaped posts, or photonic crystal structures. Other examples oftwo-dimensional structures include curved sided cone structures asdescribed in U.S. Patent Application Publication No. 2010/0128351,incorporated herein by reference. FIG. 3 is a perspective viewillustrating one embodiment of 2D periodic structures 36, in thisexample pyramids, on a substrate 34.

Extraction elements arranged as a periodic structure with a singlespacing between extraction elements may be referred to as single-pitchor single-period structures. An alternative configuration of extractionelements, referred to as multi-pitch or multi-periodic structures, isextraction elements, typically engineered nanostructures, arranged intomultiple zones with different periodic characteristics in each zone.FIGS. 4A-4E illustrate various configurations of zones of multi-periodicstructures having at least different pitches. A zone is a plurality ofsets of extraction elements proximate one another and non-overlapping.The sets can be directly adjacent one another, or adjacent one anotherand separated by a gap. Each set is a plurality of extraction elementsadjacent one another with a periodic characteristic, and each set in azone has a different periodic characteristic from the other sets in thezone. The extraction elements in each set are thus not random and arenot non-periodic. The zone repeats throughout the nanostructured surfaceof the light extraction film. In particular, the same plurality of setsin a zone repeats, resulting in a repeating variable periodiccharacteristic of the extraction elements. The plurality of extractionelements in a set can include as few as two extraction elements, inwhich case the pitch (when used as the multi-periodic characteristic) isonly the single distance between the two extraction elements in the set.

Examples of periodic characteristics include pitch, height, aspectratio, and shape. Pitch refers to the distance between adjacentextraction elements, typically measured from their topmost portions.Height refers to the height of the nanostructures measured from theirbase (in contact with the underlying layer) to the topmost portion.Aspect ratio refers to the ratio of the cross-sectional width (widestportion) to height of the extraction elements. Shape refers to thecross-sectional shape of the extraction elements.

Controlling pitch through multi-pitch zones has been found to providebetter angular distribution of OLED light extraction when compared withusing a single pitch. Also, using multi-pitch zones provides for moreuniform OLED light extraction and allows for tuning the light extractionfor specific colors. The light extraction films thus use multi-periodiczones of pitch and may combine the multi-pitch zones with othermulti-periodic characteristics such as those described above.

FIGS. 4A-4E show prisms (or pyramids) as the extraction elements forillustrative purposes. Extraction elements can include other types of 1Dand 2D features, such as those described above.

FIG. 4A illustrates nanostructured surface 722 with a zone having setsof extraction elements 724, 726, and 728. Each of the sets 724, 726, and728 has a different pitch and feature height compared to the pitches andfeature heights of the other sets in the zone. Set 724 has a periodicpitch 730, set 726 has a periodic pitch 732, and set 728 has a periodicpitch 734. The pitches 730, 732, and 734 do not equal each other. In oneparticular embodiment, pitch 730=0.420 microns, pitch 732=0.520 microns,and pitch 734=0.630 microns. The sets 724, 726, and 728 constituting thezone would then repeat to form the nanostructured surface of the lightextraction film.

FIG. 4B illustrates nanostructured surface 736 with a repeating zonehaving sets of extraction elements 738, 740, and 742 each having aperiodic pitch and feature height different from the other sets. Innanostructured surface 736, the zone is shown repeated twice. Thisexample has fewer features in each set compared with the sets in FIG.4A.

FIG. 4C illustrates nanostructured surface 744 with a repeating zonehaving sets of extraction elements 746, 748, and 750 each having aperiodic pitch and feature height different from the other sets. Innanostructured surface 744, the zone is shown repeated eight times. Thisexample has fewer features in each set compared with the sets in FIGS.4A and 4B.

FIG. 4D illustrates nanostructured surface 752 with a repeating zonehaving sets of extraction elements 754 and 756 each having periodic apitch and feature height different from the other set. In nanostructuredsurface 752, the zone is shown repeated three times. This exampleillustrates a zone having two sets compared with the zones having threesets in FIGS. 4A-4C.

FIG. 4E illustrates nanostructured surface 758 with a zone having setsof extraction elements 760, 762, and 764. Each of the sets 760, 762, and764 has a different pitch and feature height compared to the pitches andfeature heights of the other sets in the zone. Set 760 has a periodicpitch 766, set 762 has a periodic pitch 768, and set 764 has a periodicpitch 770. The pitches 766, 768, and 770 do not equal each other. In oneparticular embodiment, pitch 766=0.750 microns, pitch 768=0.562 microns,and pitch 770=0.375 microns. The sets 760, 762, and 764 constituting thezone would then repeat to form the nanostructured surface of the lightextraction film. This example illustrates a varying pitch in a zoneincreasing in a different direction compared with the varying pitch inthe sets of FIG. 4A.

Aside from pitch and feature height, multi-periodic zones can have setsof other multi-periodic characteristics. FIG. 4F illustratesnanostructured surface 772 having sets of extraction elements withmulti-periodic aspect ratios. The repeating zone for nanostructuredsurface 772 includes sets 774 and 776 with the extraction elements inset 774 having a different aspect ratio from the extraction elements inset 776. As another example, FIG. 4G illustrates nanostructured surface778 having sets of extraction elements with multi-periodic shapes. Therepeating zone for nanostructured surface 778 includes sets 780 and 782with the extraction elements in set 780 having a different shape fromthe extraction elements in set 782. In this example, the extractionelements in set 780 can be 1D square ridges or 2D square posts, whilethe extraction elements in set 782 can be 1D elongated prisms or 2Dpyramids.

The extraction elements in FIGS. 4A-4G are illustrative of periodiccharacteristics and zones. A zone can have two, three, or more sets ofextraction elements with a periodic characteristic in each set anddifferent from the values of the same periodic characteristic in theother sets. In FIGS. 4A-4E, the different pitches among sets in a zoneare accomplished using extraction elements of different heights.However, the height of the extraction elements can be the same while thepitch among sets is different. The sets in a zone can thus have one ormore different periodic characteristics among them.

Light extraction elements can also be formed from nanoparticles or fromthe combination of nanoparticles and regular or random elementsseparately created on a light extraction film substrate. FIG. 5 is adiagram of the construction of one illustrative light extraction film 10having periodic structures with nanoparticles positioned on the periodicstructures. In the embodiment shown in FIG. 5, the extraction elementsare the combination of the periodic structures and the nanoparticles.Light extraction film 10 includes a substantially transparent (flexibleor rigid) substrate 12, low index periodic structures 14, optionalnanoparticles 16 are preferably dispersed in a surface layer manner overperiodic structures 14, and a high index planarizing backfill layer 18forming a substantially planar surface 19 over periodic structures 14and nanoparticles 16.

FIG. 6 is a diagram of the construction of another light extraction film20 having periodic structures and nanoparticles. Light extraction film20 includes a substantially transparent (flexible or rigid) substrate22, low index periodic structures 24, nanoparticles 26, and a high indexplanarizing backfill layer 28 forming a substantially planar surface 29over periodic structures 24 and nanoparticles 26. In this embodiment,nanoparticles 26 are distributed throughout backfill layer 28, such asin a volume distribution, rather than in a surface layer manner as shownfor light extraction film 10.

The optional nanoparticles, also referred to as sub-micron particles,for light extraction films 10 and 20 have a size within the range fornanostructures and can be the same size or different sizes within thatrange for a particular film. The nanoparticles are also light scatteringwhen the nanoparticles are within a particular size range and have adifferent index of refraction from the backfill layer, as furtherexplained below. For example, the nanoparticles can have diameters inthe range of 100 nm to 1,000 nm, or the nanoparticles can have diametersin the range of 10 nm to 300 nm and form agglomerations with sizes inthe range of 100 nm to 1,000 nm. Furthermore, the nanoparticles cancomprise mixed particles sizes, large and small nanoparticles mixedtogether such as 300 nm nanoparticles mixed with 440 nm or 500 nmnanoparticles, which can result in an increased spectral response of thecorresponding light extraction film. The nanoparticles can possibly havesizes outside the range for nanostructures depending upon a particularapplication. For example, if the light extraction film is used for OLEDlighting, as opposed to displays, then the nanoparticles can havediameters up to several microns. The nanoparticles can be composed oforganic materials or other materials, and they can have any particleshape, regular or irregular. The nanoparticles can be porous particles.Examples of nanoparticles used in light extraction films are describedin U.S. Patent Application Publication No. 2010/0150513, incorporatedherein by reference.

For light extraction film 10 having optional nanoparticles 16distributed in a surface layer manner, the layer of nanoparticles can benanoparticles in a monolayer, with a layer having agglomerations ofnanoparticles, or in a multi-layer. The nanoparticles can be coatedwithout use of a binder, which can result in the agglomerations ofnanoparticles. In a preferred embodiment, nanoparticles 16 have a size,for example diameter, substantially equal to or slightly less than thepitch (e.g., one-fourth to one times the pitch) of periodic structures14 such that the nanoparticles are at least partially ordered by theperiodic structures. The at least partial ordering can occur through theparticles becoming aligned or assembled within the periodic structures.The pitch of the periodic structures refers to the distance betweenadjacent structures, for example the distance between the apexes ofadjacent prisms. Size matching can be used to achieve the at leastpartial ordering, for example 440 nm nanoparticles with 600 nm pitchperiodic structures or 300 nm nanoparticles with 500 nm pitch periodicstructures. In addition, the shape and aspect ratio of the periodicstructures can be factors in determining the size matching and partialordering of the nanoparticles.

The planarizing backfill layers for light extraction films (e.g. 10, 20and 716) are applied over the extraction elements to planarize them andprovide for index contrast. Low index extraction elements with a highindex backfill layer means that backfill layer has a higher index ofrefraction than the extraction elements and that the backfill layer andextraction elements have a sufficient difference in refractive indices,preferably 0.2 or greater, to enhance light extraction of an OLED devicein optical communication with the light extraction films. The lightextraction film can be in optical communication with the OLED device byhaving the planar surface of the backfill layer placed against, eitherdirectly or through another layer, the light output surface of the OLEDdevice. The planarizing backfill layer can optionally be an adhesive forbonding the light extraction film to the light output surface of theOLED device. Examples of high index backfill layers for light extractionfilms are described in U.S. Patent Application Publication No.2010/0110551, incorporated herein by reference.

Materials for the substrates, low index extraction elements, high indexbackfill layers, and optional nanoparticles for light extraction films(e.g. 10 and 20) are provided in the published patent applicationspreviously cited. For example, the substrate can be glass, PET,polyimides, TAC, PC, polyurethane, PVC, or flexible glass. Processes formaking light extraction films (e.g. 10, 20 and 716) are also provided inthe published patent applications identified above. Optionally, thesubstrate can be a barrier film to protect a device incorporating thelight extraction film from moisture or oxygen. Examples of barrier filmsare disclosed in U.S. Patent Application Publication No. 2007/0020451and U.S. Pat. No. 7,468,211; incorporated herein by reference.

FIG. 7 illustrates light extraction film 142 incorporated into a topemitting OLED device 120. The Table below describes elements of device120 and the arrangement of those elements, as identified by thereference numbers provided in FIG. 7. The configuration shown in FIG. 7is provided for illustrative purposes only, and other configurations ofOLED display devices are possible. Light extraction film 142 includes asubstantially transparent substrate 122 (flexible or rigid), optionalbarrier layer 124, low index extraction elements 126, and a high indexplanarizing backfill layer 128 forming a substantially planar surfaceover extraction elements 126. Applying a light extraction film to anOLED device means that the light extraction film is placed at anappropriate location within the OLED device as, for example, describedin FIG. 7 and the Table below.

Top Emitting OLED Device with Light Extraction Film Ref. No. Type ofElement 121 optional functional layers 122 light extraction filmsubstrate 124 optional barrier layer 126 low index structure 128 highindex backfill 130 optical coupling layer 132 electrode 1 134 optionalthin film encapsulant layer or optional capping layer 136 organic layers138 electrode 2 140 device substrate 142 light extraction film

In one embodiment, a method for coupling an optical film is described.The method comprises providing an optical film having a surface layerhaving a refractive index of at least 1.60; providing a substrate;applying an optical coupling layer to the surface layer of the opticalfilm, the substrate, or a combination thereof; and laminating theoptical film to the substrate forming a laminated optical construction.As will subsequently be described in greater detail, the opticalcoupling layer comprises at least 40 wt.-% inorganic nanoparticleshaving a refractive index of at least 1.85, and a polymeric silanesurface treatment;

FIGS. 8 and 9 illustrate some embodied methods laminating an (e.g. lightextraction) optical film to a substrate (e.g. OLED device) by use of anoptical coupling layer forming a laminated optical construction.

As shown in FIG. 8, an optical coupling layer 42 is applied to a planarsurface 48 of the backfill layer in a light extraction film 44, whichcan then be laminated to a light output surface 46 of an OLED device 40.The optical coupling layer can be an adhesive providing for opticalcoupling between the light output surface of the OLED device and thebackfill layer of the light extraction film. Use of an adhesive as theoptical coupling layer along with a lamination process can also serve toadhere the light extraction film to the OLED device and remove air gapsbetween them. The backplane morphology of the OLED device is typicallynon-planar, as represented by pixel wells 47, and optical coupling layer42 is expected to conform to or expand into the pixel well geometryfilling the gap between light extraction film 44 and OLED device 40.

Alternatively, as shown in FIG. 9, an optical coupling layer 52 isapplied to a light output surface 56 of an OLED device 50, and a planarsurface 58 of the backfill layer in a light extraction film 54 is thenlaminated to OLED device 50. If the adhesive optical coupling layer isapplied to the OLED device before lamination of the light extractionfilm, as shown in FIG. 9, the optical coupling layer can also serve toplanarize the light output surface of the OLED device. For example, atop emitting active matrix OLED display backplane does not necessarilyhave a high degree of planarity, as represented by pixel wells 57, inwhich case the optical coupling layer can be pre-deposited onto thecathode or any other top layer of the OLED stack prior to lamination ofthe light extraction film. Such pre-deposition of the optical couplinglayer can reduce non-planarity of the backplane and the device, allowingfor subsequent lamination of the light extraction film. The opticalcoupling layer in this case can be coated onto the OLED display withsolution deposition methods. For example, it can be applied onto theentire area of the OLED from a liquid formulation, in which case afterlamination of the light extraction film it can be optionally cured usingUV or thermal curing methods. It can also be laminated as an opticalcoupling film provided separately between two liners with prior removalof the liner facing the OLED device, in which case it is expected toconform or expand into the pixel wells. After application of the opticalcoupling layer a sufficient planarization over the backplane morphologyis produced as shown in FIG. 9.

Since the backplane morphology determines the distance between theextraction elements (nanoparticles and periodic structure) and OLEDdevices, the materials for the optical coupling layer typically have ahigh index of refraction, at least 1.65 or 1.70 up to 2.2 comparable tothat of OLED organic and inorganic layers (e.g., ITO).

The axial gain (as measured according to the test method described inthe examples) is typically at least 1.5 or 2. In some embodiments, theaxial gain is no greater than about 3. Further, the integrated gain maybe at least 1.5, or 1.6, or 1.7. In some embodiments, the axial gain isno greater than about 2.

In addition to having the proper refractive index, the optical couplinglayer must be sufficiently transparent with a transmission of at least80% or 85%. Typically the haze is no greater than 10% or 5%. Further,the optical coupling layer must sufficiently adhere to both the (e.g.top emitting) OLED device and the light extraction film (e.g. backfilllayer).

The methods just described can produce one class of laminated opticalconstructions. In another embodiment, the laminated optical constructionis an intermediate. In this embodiment, the substrate may be a releaseliner For example, light extraction film 44 of FIG. 6 comprising opticalcoupling layer 42 applied to planar surface 48 may temporarily furthercomprise a release liner releasably attached to optical coupling layer43. This intermediate may then be provided to an OLED manufacturer thatremoves the release liner and bonds the optical coupling layer to anoptical substrate such as an organic light emitting diode (OLED) device.

Also described are coating compositions suitable for use as an opticalcoupling layer of an OLED device or other optical device wherein a highrefractive index optical coupling layer is desired.

The coating composition comprises high refractive index inorganicnanoparticles. Such inorganic nanoparticles have a refractive index ofat least 1.85, 1.90, 1.95, 2.00 or higher.

Various high refractive index nanoparticles are known, including forexample zirconia (“ZrO₂”), titania (“TiO₂”), antimony doped tin oxides,tin oxides, alone or in combination. Mixed metal oxide may also beemployed. In some favored embodiments, the inorganic nanoparticles are“titania nanoparticles”, that refers to a nanoparticles having at leasta titania core. Typically substantially the entire nanoparticleincluding the surface is entirely titania.

High index metal oxide sols can be favored since such are easier tosurface treat and remain well dispersed. Zirconias sols are availablefrom Nalco Chemical Co. under the trade designation “Nalco 00SS008”,Buhler AG Uzwil, Switzerland under the trade designation “Buhlerzirconia Z-WO sol” and Nissan Chemical America Corporation under thetrade name NanoUse ZR™. Zirconia nanoparticles can also be prepared suchas described in U.S. Patent Publication No. 2006/0148950 and U.S. Pat.No. 6,376,590. A nanoparticle dispersion that comprises a mixture of tinoxide and zirconia covered by antimony oxide (RI˜1.9) is commerciallyavailable from Nissan Chemical America Corporation under the tradedesignation “HX-05M5”. A tin oxide nanoparticle dispersion (RI˜2.0) iscommercially available from Nissan Chemicals Corp. under the tradedesignation “CX-S501M”. Less preferred TiO₂ sols are available typicallydispersed in strong acid or base condition such as the TiO₂ sol underthe trade designation STS-01 from Ishhihara Sangyo Kaisha Ltd. TiO₂sols, commercially available from Showa Denko Corp under the tradedesignation NTB-01 and from Taki chemical Co. Ltd under the tradedesignation AM-15, are stable sols with weak acid (ph=4˜5) can bepreferred sols.

Generally, the nano-sized particles have an average core diameter ofless than 100 nm, and more typically less than 50 nm. In someembodiments, the nano-sized particles have an average core diameter ofat least 5 nm. In some embodiments, the nano-sized particles have anaverage core diameter ranging from 10 to 20 nm.

Although other methods such as titration and light scattering techniquesmay be used, the particle size referred to herein is based ontransmission electron microscopy (TEM). Using this technique, TEM imagesof the nanoparticles are collected, and image analysis is used todetermine the particle size of each particle. A count-based particlesize distribution is then determined by counting the number of particleshaving a particle size falling within each of a number of predetermineddiscrete particle size ranges. The number average particle size is thencalculated. One such method is described in U.S. Provisional Application61/303,406 (“Multimodal Nanoparticle Dispersions, Thunhorst et al.)filed 11 Feb. 2010, and will be referred to herein as the “TransmissionElectron Microscopy Procedure”.

According to the Transmission Electron Microscopy Procedure, to measurethe particle size and particle size distribution, a nanoparticle sol isdiluted by taking 1 or 2 drops of sol and mixing it with 20 mL ofdeionized distilled water. The diluted samples are sonicated (UltrasonicCleaner, Mettler Electronics Corp., Anaheim, Calif.) for 10 minutes anda drop of the diluted sample is placed on a 200 mesh Cu TEM grid with acarbon/Formvar film (Product 01801, Ted Pella, Inc, Redding, Calif.),and dried at ambient conditions. The dried samples are imaged using aTransmission Electron Microscope (TEM) (HITACHI H-9000NAR, Hitachi,Ltd., Tokyo, Japan) at 300 kV with magnifications ranging from 10K timesto 50K times depending on the particle sizes in each sample. Images arecaptured using Gatan Digital Micrograph software on a CCD camera(ULTRASCAN 894, Gatan, Inc., Pleasanton, Calif.). Each image has acalibrated scale marker. Particle sizes are measured using a single linethrough the center of each particle; thus, the measurements are based inthe assumption that the particles are spherical. If a particularparticle is non-spherical, the measurement line is taken through thelongest axis of the particle. In each case, the number of measurementstaken on individual particles exceeds that stipulated in the ASTM E122test method for the error level of 5 nm.

The optical coupling layer comprises a relatively high concentration ofinorganic nanoparticle having a refractive index of at least 1.85. Theoptical coupling layer typically comprises at least 40 wt.-% of suchinorganic nanoparticles. In some embodiments, the concentration of highrefractive index nanoparticle is at least 45 wt.-%, 50 wt.-%, or 55wt.-%. Typically the concentration of inorganic nanoparticles is nogreater than about 75 wt.-% or 70 wt.-%.

The high refractive index nanoparticles are surface treated with apolymeric silane surface treatment.

Generally, a “polymeric silane surface treatment” comprises polymerizedor copolymerized repeat units and alkoxy silane groups. The alkoxygroups react with hydroxy groups on the surface of a titaniananoparticle forming a covalent bond between the surface treatment agentand the titania surface.

The polymeric silane surface treatment generally comprises a lowmolecular weight polymer. In some embodiments, the polymeric silanesurface treatment has a weight average molecular weight of at least 1000gm/mole, or 1500 gm/mole, or 2000 gm/mole. The weight average molecularweight of the polymeric silane surface treatment is typically no greaterthan 20,000 gm/mole, 10,000 gm/mole, or 5,000 gm/mole. For the polymericsilane surface treatment, the weight average molecular weight iscalculated according to Gel Permeation Chromatography (GPC).

The polymeric silane surface treatment typically comprises a (e.g.random) acrylic copolymer comprising the reaction product of one or more(meth)acrylate monomers. As used herein, “(meth)acrylate” refers to anacrylate and/or methacrylate.

The acrylic copolymer comprises repeat units derived from one or morefirst alkyl (meth)acrylates comprising 4 to 18 carbon atoms. In someembodiments, the acrylic copolymer comprises at least 50 wt. %, or 60wt. %, or 70 wt.-% of repeat units derived from alkyl (meth)acrylateshaving 4 to 18 carbon atoms based on the total weight of the acryliccopolymer. In some embodiments, the acrylic copolymer comprises nogreater than 98 wt. %, or 95 wt. % of repeat units derived from alkyl(meth)acrylates containing 4 to 18 carbon atoms. In some embodiments,the acrylic copolymer comprises repeat units derived from first alkyl(meth)acrylates having at least 6 carbon atoms. In some embodiments, theacrylic copolymer comprises repeat units derived from first alkyl(meth)acrylates having at least eight carbon atoms, (e.g., isooctyl(meth)acrylate and/or 2-ethylhexyl (meth)acrylate) and typically nogreater than 12 carbon atoms.

The high concentration of alkyl (meth)acrylates containing at least 4,5, 6, 7, or 8 carbon atoms contributes to the low glass transitiontemperature (Tg) of the polymeric silane surface treatment. In someembodiments, the Tg of polymeric silane surface treatment is less than−20° C., or −30° C., or −40° C., or −50° C., or −60° C. The Tg ofpolymeric silane surface treatment is typically at least −80° C.

When the polymeric silane surface treatment is utilized as a surfacetreatment on the high refractive index nanoparticles, the inclusion ofthe nanoparticles, optionally in combination with a crosslinker,typically raises the Tg by at least about 10° C., or 15° C., or 20° C.Thus, the surface treated high index particle composition (e.g. opticalcoupling layer) typically has a Tg of less than 0° C., or −10° C., or−20° C., or −30° C., or −40° C. The Tg of the surface treated high indexparticle composition is typically at least −60° C.

In some embodiments, the polymeric silane surface treatment comprisesrepeat units derived from at least one alkyl (meth)acrylate thatcontains less carbon atoms than the first alkyl (meth)acrylate. In someembodiments, the polymeric silane surface treatment comprises repeatunits derived from at least one alkyl (meth)acrylate having 1-3 carbonatom or 1-2 carbons atoms, (e.g. ethyl acrylate). In some embodiments,the acrylic copolymers comprise at least 1 wt. %, or 2 wt. %, or 3 wt.-%of repeat units derived from alkyl (meth)acrylates containing 1-3 carbonatoms or 1-2 carbon atoms based on the total weight of the acryliccopolymer. In some embodiments, the polymeric silane surface treatmentcomprises no greater than 20 wt. %, or 15 wt. %, or 10 wt. %, repeatunits derived from alkyl (meth)acrylates containing 1-3 carbon atoms, or1-2 carbon atoms. In some embodiments, such short chain alkyl(meth)acrylates may further comprise a hydroxyl group. For example, byuse of a hydroxy-alkyl acrylate, pendant hydroxy functionality can beincorporated into the polymeric silane surface treatment. Such pendanthydroxy functionality can be crosslinked with a hydroxy-reactivecrosslinker such a polyisocyanate or an epoxy.

In some embodiments, the polymeric silane surface treatment comprisesrepeat units derived from a vinyl carboxylic acid such as acrylic acid,methacrylic acid, itaconic acid, maleic acid, fumaric acid, andβ-carboxyethylacrylate. In some embodiments, the acrylic copolymerscomprise at least 0.1% wt. %, or 0.2 wt. %, or 0.3 wt.-% of repeat unitderived from vinyl carboxylic acid (e.g. acrylic acid) based on thetotal weight of the acrylic copolymer. When the polymeric silane surfacetreatment comprises repeat units derived from a vinyl carboxylic acid,the polymer comprises pendant carboxylic acid groups than can becrosslinked with a carboxylic acid-reactive crosslinker such as anaziridine or melamine crosslinker.

In some embodiments, the polymeric silane surface treatment comprisesrepeat units comprising pendant reactive groups such as hydroxyl groups,acid groups, or amine groups. The acrylic polymer typically comprises nogreater than 15 wt. % or 10 wt. %, and in some embodiments, no greaterthan 5 wt. %, or 4 wt. %, or 3 wt. %, or 2 wt. %, or 1 wt-% of monomerscontributing such pendant reactive groups Such pendant functionality canbe crosslinked with a crosslinker. The concentration of crosslinker istypically at least 0.1 wt-% and no greater than 5 wt. %, or 4 wt. %, or3 wt. %, or 2 wt. %, or 1 wt-%. Thus, the polymeric silane surfacetreatment comprises a relatively low level of crosslinking.

The polymeric silane surface treatment comprises a terminal alkoxysilane group. One approach to incorporating terminal alkoxy silanegroups into the polymer is by use of 3-mercaptopropyl trimethoxysilane.This compound is commonly used as a chain transfer agent and anend-capping unit in the polymerization of acrylic copolymers.

In some embodiments, the polymeric silane surface treatment may compriserepeat units derived from one or more other (meth)acrylate monomer. Insome embodiments, a (e.g. (meth)acrylate) monomer having a refractiveindex of at least 1.50, or 1.51, or 1.52, or 1.53, or 1.54 or greatermay be employed to raise the refractive index of the polymeric silanesurface treatment and thus optical coupling layer comprising such.Various high refractive index monomers are known. Such monomerstypically comprise at least one aromatic group and/or sulfur atoms.Typically the concentration of these other (meth)acrylate monomers is nogreater than 10-wt-% or 5-wt-% of the optical coupling composition.

The high index particles may optionally comprise a second surfacetreatment that is not a polymeric surface treatment. Generally,non-polymeric surface modifying agents do not have any polymerized orcopolymerized repeat units. In some embodiments, the non-polymericsurface modifying agents have molecular weight of less than 1500gm/mole, or less than 1000 gm/mole, or less than 500 gm/mole. Examplesof non-polymeric surface modifying agents include trialkoxy alkylsilanes and trialkoxy aryl silanes. In some embodiments, a non-polymericsurface treatment has a refractive index of at least 1.50, or 1.51, or1.52, or 1.53, or 1.54. Inclusion of a high index surface treatment cancontribute to the high refractive index of the surface modified highrefractive index nanoparticles. Phenyltrimethoxy silane is one exampleof a suitable non-polymeric surface treatment. The concentration ofnon-polymeric surface treatment is generally relatively low as comparedto the polymeric silane surface treatment. For example, theconcentration is typically no greater than 5 wt.-%, or 7.5 wt-%, or 10wt-% of the surface modified nanoparticles.

In some embodiments, the coating composition may consist entirely of thesurface treated inorganic nanoparticles. Thus, the polymeric silanesurface treatment may be the sole polymeric component of the opticalcoupling layer. The optical coupling layer typically comprises at least30 wt. %, or 31 wt. %, or 32 wt. %, or 33 wt. %, or 35 wt-% of polymericsilane surface treatment. In some embodiments, the concentration ofpolymeric silane surface treatment in the optical coupling layer is nogreater than 60 wt. %, or 55 wt. %, or 50 wt. %, or 45 wt. %. In thisembodiment, the coating composition may be substantially free of(meth)acrylate components (e.g. monomers and oligomers), particularlythose having a molecular weight of 1,000 g/mole or less. Bysubstantially free, it is meant that the composition comprises nogreater than 5 wt. %, or 4 wt. %, or 3 wt. %, or 2 wt. %, or 1 wt-% ofsuch (meth)acrylate components. It has been found that the inclusion ofappreciable amounts of such monomers can crack the OLED device duringcuring. However, small concentrations of higher molecular weightmonomers (greater than 1,000 g/mole) and especially polymers, commonlyreferred to as polymeric binders may be added. In some embodiments, theoptical coupling layer may comprise up to 10 wt-% of polymeric binders.However, in favored embodiments, the optical coupling composition isfree of polymeric binders.

Although the properties of the PSAs can be modified with commonadditives such as tackifiers and plasticizers, in some favoredembodiments coating composition useful as an optical coupling layercomprises little or no tackifiers and plasticizers. In some embodiments,the total amount of tackifier in combination with plasticizer is nogreater than 10 wt.-%, or 5 wt.-%, or 2 wt. %, or 1 wt. %.

The surface modified high index nanoparticles are generally prepared bycombining a weakly acid sol (pH=4-5) with the polymeric silane surfacetreatment and optional non-polymeric surface treatment. The mixture wasthen heated for overnight to complete the coupling reaction at theparticle surfaces. After that, the polymer modified particles wastransferred into organic solvents after removing all the water usingrotary evaporator.

The solvent is typically removed either prior to applying to the (e.g.light extraction) optical films or prior to applying the opticalcoupling layer to a substrate (e.g. OLED). Hence, the optical couplinglayer is substantially solvent free when laminated. By substantiallysolvent free it is mean that the topical coupling layer comprises lessthan 1 wt.-% solvent. It has been found that the inclusion ofappreciable amounts of solvents can render the OLED inoperable overtime.

In some embodiments, the dried and optionally cured coating compositionsexhibit pressure sensitive adhesive properties. One characteristic of apressure sensitive adhesive is tack. The probe tack of the opticalcoupling layer composition (as measured according to the test methoddescribed in the forthcoming examples) is typically at least 5 grams. Infavored embodiments, the tack is at least 30, 40 or 50 grams. In someembodiments the tack is no greater than 150 or 100 grams. Anothercharacteristic of a pressure sensitive adhesive composition is peelforce. The peak peel force (as measured according to the test methoddescribed in the forthcoming examples) is typically at least 40, or 50or 60 grams/cm and in some embodiments, at least 70 or 80 grams/cm. Insome embodiments, the peak peel force is no greater than about 200 or150 grams/cm. The minimum peel force is typically ranges from 1 or 2grams/cm to 10, 15, or 20 grams/cm. The average peel force is typicallyat least 10 or 15 grams/cm and in some embodiments at least 20 or 30grams/cm. In some embodiments, the average peak force is no greater than100, or 80, or 60 grams/cm.

EXAMPLES

All parts, percentages, ratios, etc. in the examples are by weight,unless noted otherwise. Solvents and other reagents used were obtainedfrom Sigma-Aldrich Chemical Company; Milwaukee, Wis. unless specifieddifferently.

Materials

Abbreviation/product name Description Available from 3-mercaptopropylChain Transfer Agent, 95% Alfa Aesar, Ward trimethoxysilane Hill, MABis[4-(2,3- Epoxy with a high refractive Sumitomo Seika,epoxypropylthio)phenyl]sulfide index (RI = 1.67) Hyogo, Japan DER331Epoxy Resin Dow Chemical Company, Midland, Michigan Desmodur ® N3300Aliphatic polyisocyanate Bayer Material Science, Pittsburgh, PA DMAEMA2-(Dimethylamino)ethyl Sigma-Aldrich methacrylate Chemical Company,Milwaukee, WI Isooctyl Acrylate Isooctyl Acrylate Sigma-Aldrich ChemicalCompany, Milwaukee, WI hydroxyethyl acrylate hydroxyethyl acrylate AlfaAesar, Ward Hill, MA ethyl acetate solvent Honeywell International,Inc., Morristown, NJ. IPDI Isophorone diisocyanate Toyo ChemicalIndustry Co., Ltd, Tokyo, Japan NTB-1 15% wt aqueous titanium DenkoCorporation, dioxide sol with pH at 4 Japan PHOTOMER 6210 aliphaticurethane diacrylate Cognis Corporation, Cincinnati, OHPhenyltrimethoxysilane Silane surface treatment, 97% Alfa Aesar, WardHill, MA PM 1-methoxy-2-propanol Alfa Aesar, Ward Hill, MA SR238 1,6hexanediol diacrylate Sartomer Company, Exton, PA Vazo 67 2,2′-Azobis(2-Sigma-Aldrich methylbutyronitrile) Chemical Company, Milwaukee, WIVarious silane functional polymers were prepared by solutionpolymerization in ethyl acetate (“EthAc”) as follows.

Preparative Examples

Synthesis of Silane Functional Polymers

Synthesis of Polymer-I In an 8 ounce bottle, 27 g of isooctyl acrylate,3.0 g of hydroxyethyl acrylate, 7.4 g of 3-mercaptopropyltrimethoxysilane, 80 g ethyl acetate, and 0.15 g of Vazo 67 were mixedtogether. The mixture was bubbled under N₂ for 20 min, then, the mixturewas placed in an oil bath at 70° C. for 24 hours. This resulted in anoptical clear solution with wt % solids of 30.9%.Synthesis of Polymer-II

In an 8 ounce bottle, 27 g of isooctyl acrylate, 3.0 g of hydroxyethylacrylate, 3.7 g of 3-mercaptopropyl trimethoxysilane, 80 g ethylacetate, and 0.15 g of Vazo 67 were mixture together. The mixture wasbubbled under N₂ for 20 min, then, the mixture was placed in an oil bathat 70° C. for 24 hours. This resulted in an optical clear solution witha wt % solids of 31.04%.

Synthesis of Polymer-III

In an 8 ounce bottle, 27 g of isooctyl acrylate, 3 g of DMAEMA, 3.7 g of3-mercaptopropyl trimethoxysilane, 80 g ethyl acetate, and 0.15 g ofVazo 67 were mixture together. The mixture was bubbled under N₂ for 20min, then, the mixture was placed in an oil bath at 70° C. for 24 hours.This resulted in an optical clear solution with a wt % solids of 30.8%.

Synthesis of Polymer-IV

In an 8 ounce bottle, 29.4 g of isooctyl acrylate, 0.6 g of acrylicacid, 3.7 g of 3-mercaptopropyl trimethoxysilane, 80 g ethyl acetate,and 0.15 g of Vazo 67 were mixture together. The mixture was bubbledunder N₂ for 20 min, then, the mixture was placed in an oil bath at 70°C. for 24 hours. This resulted in an optical clear solution with wt %solids of 30.8%.

Preparation of Backfilled Light Extraction Film

A nanostructured film fabricated by first making a multi-tipped diamondtool using focused ion beam (FIB) milling as described in U.S. Pat. No.7,140,812. The diamond tool was then used to make a coppermicro-replication roll which was then used to make 400 nm-pitch lineartriangular-waveform structures on a PET film in a continuous cast andcure process utilizing a polymerizable resin made by mixing 0.5% (2,4,6trimethyl benzoyl) diphenyl phosphine oxide into a 75:25 blend ofPHOTOMER 6210 and SR238. The nanostructured film was backfilled with anapproximately 2 μm thick high-refractive index backfill layer asdescribed in US Patent Application Publication 2012/0234460.

Test Methods

Tack Measurement

A TA.XT Plus Texture Analyzer (available from Texture Technologies Corp,Scarsdale, N.Y.) with a 6 mm hemispheric probe was used for tacktesting. The following settings were used: pre-test speed 0.50 mm/sec,test speed 0.01 mm/sec, post test speed 0.05 mm/sec, applied force 100.0grams, return distance 5.00 mm, contact time 30 sec, trigger type auto,trigger force 5.0 grams, tare mode auto, proportional gain 50, integralgain 20, differential gain 5, and max tracking speed 0.00 mm/sec.

The tests were conducted as follows. A 12.7 cm×2.5 cm (5 inch×1 inch)strip of coated sample taken from a middle section of a coating waslaminated to the back of a 0.64 cm (¼ inch) thick by 2.5 cm×15.2 cm (1inch×6 inch) bar and slid into a holding fixture directly underneath thetest probe. The probe was allowed to sit on sample for 30 seconds aftermaking contact to allow the relaxation of the coating. Four measurementswere taken along each sample strip. If a data point was an outlier itwas discarded and the average peak force determined from the remainingdata.

Peel Tests

Samples were prepared by coating the optical coupling solution onto thebackfill side of the backfilled light extraction film described above.The light extraction film was taped down to a flat surface and thecoating was applied with a #30 Meyer bar. The coating was heated at 65°C. for 10 minutes. All coatings yielded a dry adhesive thickness of10-12 microns. The dried coating was then laminated to a barrier filmusing a hand roller. The barrier film was as described in Example 1 ofU.S. Pat. No. 7,468,211. T-peel tests were conducted on an IMASS SP-2000slip-peel tester (from Instrumentors Inc., Strongsville Ohio) with 2.5cm (1 inch) wide strips at a peel rate of (5 inch/min) over 25 seconds.The peak force, the minimum force occurring after the first peak, andthe average of the force over the 25 second test were recorded andaveraged over three test samples.

Shear Tests

Shear test samples were prepared by coating optical coupling materialson light extraction film as described for the Peel Test. The films werethen cut and adhered to a stainless steel plate with a contact area of1.3 cm×1.3 cm (0.5 inch×0.5 inch) or 2.5 cm×2.5 cm (1 inch×1 inch). Theexcess tape strip was fastened to either a 0.5 kg or 1 kg weight. Theassemblies were allowed to hang vertically, therefore measuring theshear of the adhesive. The time required for the adhesive to fail wasrecorded.

Molecular Weight

The weight average, (Mw) molecular weight of each of the polymers wasdetermined by Gel Permeation Chromatography. Results are provided in thetable below.

Glass Transition Temperature

Samples were prepared by pouring 3 grams of the solution to be testedonto a release liner and drying at 25° C. for 18 hours and then placingthe samples into a oven at 65° C. for 10 minutes. The glass transitiontemperature was then measured using a TA Instruments (New Castle, Del.)Model Q200 Differential Scanning calorimeter (DSC) run in Modulated DSCmode.

Polymeric Silane Surface Treatments Monomers/ Weight MPTMS MW TgMonomers Ratio Ratio (g/mol) (° C.) Polymer-I IOA:HEA 90:10 80.2/19.8Polymer-II IOA:HEA 90:10 89/11 2670 −63.3 Polymer-III IOA:EMADMA 90:1089:11 3060 Polymer-IV IOA:AA 98:2  89:11 3840TiO₂ Nanoparticles Comprising a Polymeric Silane Surface Treatment

Into a 2 L round-bottom flask equipped with a dropping funnel,temperature controller, paddle stirrer, and distilling head, was charged177 g of NTB-1 sol and 200 g of 1-methoxy-2-propanol, which were mixedtogether. 3.24 g of phenyltrimethoxysilane, 30 g of toluene, and thepolymer solution specified in the table below was added under rapidstirring. After 15 min, the temperature was raised to 48° C. and anadditional 240 g of toluene was added. The mixture was then heated to80° C. for 16 hours.

The temperature was allowed to return to room temperature and themixture was then transferred into a round flask. The solvent was removedusing a rotary evaporator to yield a white wet-cake like materials. Thenan additional 400 g of toluene was added. The solvents were furtherremoved using a rotary evaporator. The final product was a dispersion ofsurface treated TiO₂ nanoparticles in toluene. The weight percent solidsin the dispersions are given in the table below.

The solutions were coated on primed PET using a glass rod. The coatedsamples were dried in a vacuum oven for 5 minutes at 65° C. Afterdrying, the samples yielded optically clear and sticky coatings withbluish color in thick areas. The tack was measured as described aboveand the refractive indexes of the materials were measured using aMetricon MODEL 2010 prism coupler (Metricon Corporation Inc. Pennington,N.J.) at 632.8 nm and are reported in the table below.

TiO₂ Surface Treated with the Silane Functional Polymers of Table 1TiO₂/ Tack Weight % Polymer (decoupling Solids of Solids force fromExam- TiO₂ Weight Tg probe, ple Polymer Dispersion Ratio RI (° C.)grams) 1 Polymer-I 33.62 69.3:30.7 1.78 6.3 2 Polymer- 36.66 59.7:40.31.71 −43.3 73.6 II 3 Polymer- 39.5 60.2:39.8 1.72 60.0 III 4 Polymer-27.58 60.2:39.8 1.73 IV

The glass transition temperature of the adhesive prepared according toExample 2 was determined according to the test method previouslydescribed and found to be −43° C. An additional glass transitiontemperature of Example 2 was observed at 65.7° C., which iscorresponding to the phenylsilane that was bonded to the nanoparticlesurfaces.

Example 5

Into a small jar, 20 g of the solution made according to Example 2 and0.168 g of Desmodur® N3300 polyisocyanate was added. The mixture wasultrasonic treated for 5 min to a good mixture. Then, the solution wascoated on a primed PET surface using a glass rod. The resulting bluishcoating was heated in an oven at 70° C. or 3 hours. The resulting filmwas found to be sticky. The refractive index was 1.69.

Example 6

Into a small jar, 10.1 g of the solution made according to Example 2 and0.0927 g of bis[4-(2,3-epoxypropylthio)phenyl]sulfide was added. Themixture was ultrasonic treated for 5 min to a good mixture. Then, thesolution was coated on a primed PET surface using a glass rod. Theresulting bluish coating was heated in an oven at 70° C. or 3 hours. Theresulting film was found to be sticky. The refractive index was 1.72.

Example 7

In a 3-necked flask, 180 g of NTB-01 TiO₂ sol (15% wt), 91 g ofPolymer-II prepared above, 230 g of PM and 50 g of toluene were addedtogether, the mixture was stirred at room temp for 30 min. Then the tempof mixture was heated to 45° C., an additional 220 g of toluene wasadded. The final mixture was heated to 80° C. for 16 hours.

Then the temperature was allowed to return to room temp. The mixture wasthen transferred into a round flask and the solvent was removed usingrotary evaporator to yield a white wet-cake like materials. Then anadditional 800 g of toluene was added. The solvents were further removedusing a rotary evaporator. The final product was a dispersion ofPolymer-II modified TiO₂ nanoparticles in toluene at about 31.8% wtsolid.

Example 7 was cast on PET film and dried at room temperature. Therefractive index of the resulting transparent sticky solid was 1.65.

Peel tests and shear tests were conducted on the Polymer-II modifiedTiO₂ solution according to the test methods previously described. Peeland shear tests were also conducted on additional samples prepared byadding 1% IPDI or 1% DER331 epoxy to the Polymer-II modified TiO₂solutions. All peels were shocky with split (cohesive failure) duringthe peak value. Cohesive failure was also observed in the shear tests.The results are as follows.

Peak Minimum Average Time to Peel Force Peel Force Peel Force ShearCross- grams/cm grams/cm grams/cm Failure* linker (oz/inch) (oz/inch)(oz/inch) (min) Example 2 None 60.2 (5.39) 3.7 (0.33) 18.2 (1.63) 22Example 8 1% IPDI 87.6 (7.85) 2.5 (0.22) 42.2 (3.78) 33 Example 9 1% 109 (9.74) 4.5 (0.40) 34.6 (3.10) 27 DER331 *Measured with 1 kg weightand 1.3 cm × 1.3 cm contact area. Samples tested with a 0.5 kg weightand 2.5 cm × 2.5 cm contact area did not fail after longer than 10,000minutes.

Coatings were prepared on primed PET for optical testing using a #30Meyer rod resulting in a coating thickness of about 10 microns. Thecoated samples were dried in a vacuum oven for 5 minutes at 65° C. Thetransmission, haze and clarity were measured using a HazeGard Plus(BYK-Gardner USA, Columbia, Md.). The measurements were taken on threesections near the central region of each sample and averaged. Theresults are reported in the table below.

Transmission Clarity Example Polymer (%) Haze (%) (%) PET No coating91.53 0.54 100.00 1 Polymer-I 85.43 1.82 99.83 2 Polymer-II 86.17 2.1099.50 3 Polymer-III 86.80 1.47 99.73 7 Polymer-II 85.83 2.90 98.9

Comparative Example C-1: Fabrication of Top Emissive OLEDs (without aLight Extraction Film and Optical Coupling Layer)

Approximately 2 nm of Chromium (Cr) and 100 nm of Silver (Ag) werepre-coated onto 0.7 mm-thick polished soda-lime glass samples (DeltaTechnologies, Stillwater, USA) substrates by standard thermal depositionin a vacuum system at base pressure of about 10⁻⁶ Torr. Subsequently, a10 nm thick Indium-Tin-Oxide (ITO) layer was vacuum sputtered underdirect current conditions (400 W forward power) onto the glass/Cr/Agsubstrates to complete the bottom OLED electrode fabrication(bottom-electrode shadow masks were used for Cr, Ag and ITO coatings).Following the ITO sputtering process, a layer of approximately 500 nmthick photoresist (TELR-P003 PM, TOK America) was spin-coated andphotolithographically patterned according to a pre-defined pattern andhard-baked at 230° C. to define a finished substrate for top-emissive(TE) OLED fabrication.

The following OLED construction was deposited for green-emissive TE OLEDdevice using shadow masks designed for organic layer depositions:

EIL (20 nm)/ETL (25 nm)/EML (30 nm)/HTL2 (10 nm)/HTL1 (165 nm)/HIL (100nm), where EIL is an electron injection layer, ETL is an electrontransport layer, EML is an emissive layer with green electroluminescencecharacteristics, HTL1 and HTL2 are hole transport layers, and MoO₃ wasused as the hole injection layer (HIL). All the layers above werefabricated by standard thermal deposition in a vacuum system at basepressure of about 10⁻⁶ Torr.

Following the organic layer deposition, approximately 80 nm thick ITOwas vacuum sputtered under direct current conditions (400 W forwardpower) using a shadow mask designed for the top-electrode.

Finally, the TE OLED device was completed by coating an additional 200nm of MoO₃ as a capping layer onto the ITO top electrode using a shadowmask similar to that used for coating OLED organic layers. The MoO₃layer was fabricated by standard thermal deposition in a vacuum systemat base pressure of about 10⁻⁶ Torr.

After completion, the TE OLEDs were encapsulated with glass cap andUV-curable epoxy (Nagase Corp., Japan) applied and cured by theperimeter of the glass cap. Moisture absorbing desiccant was includedinto the package prior to encapsulation to improve device stability.

Lamination of OLED Light Extraction Film onto Top Emitting OLED usingOptical Coupling Layer

A backfilled light extraction films was prepared as previouslydescribed. Prior to lamination, the optical coupling coatingcompositions of Examples 2-4 were coated from solutions onto backfilledlight extraction films using a Myre bar #30. Each coating was then driedin vacuum at 60° C. for 5 minutes to evaporate the solvent and to form agel optical coupling layer on the film surface and was immediatelytransferred in to an inert glovebox. This was followed by a pre-bake at80° C. for approximately 5 minutes in order to dry out any moisturecaptured during transfer into glovebox. TE OLED samples were fabricatedaccording to the procedure described in Comparative Example C-1. Priorto encapsulating the devices with glass as described in ComparativeExample C-1, the extractor films with m-based OCLs were laminated ontothe devices. Following the lamination, the devices were encapsulated asdescribed in Comparative Example C-1.

The fabricated TE OLEDs of Comparative Example C-1 and those preparedfrom Examples 2-4 were analyzed using a variety of OLED characterizationtechniques such as luminance-current-voltage (LIV) test using Keithley2400™ source meter and PR650 photopic camera (Photo Research Inc., USA),angular luminance measurements using Autronic™ Conoscope (AutronicMelchers GmbH, Karsruhe, Germany), and goniometry measurements ofefficiency and electroluminescence spectra at different viewing anglesusing PR650 camera and a manual goniometer constructed in house. In theLIV test, the devices were subjected to a DC current sweep typically inthe range of 4 to 20 mA/cm² current density. In angular conoscopic andgoniometric measurements, all devices were operated under constantcurrent corresponding to 10 mA/cm² current density for each operateddevice.

The table below gives axial and integrated optical gains of the deviceswith extractor laminated using Polymer-based OCL materials. The gainswere calculated as luminance (axial) and luminous intensity (integrated)of laminated extractor devices divided by those values of controlsamples (Comparative Example C-1) prepared on the same test coupon. Theaxial luminance and integrated luminous intensity data was obtainedusing conoscopic tests as described above. The axial gain represents theextraction efficiency along the normal viewing direction relative to thedevice light output surface, and integrated gain reflects extractionefficiency in all directions of light emitted from the light outputsurface of the OLED device.

Optical Coupling Axial Gain Composition Mean (St. Integrated GainExample Dev.) Mean (St. Dev.) Comparative C-1 1 1 No light extractionfilm 2 2.6 (0.3) 1.8 (0.2) 3 2.5 (0.6) 1.8 (0.4) 4 2.3 (0.1) 1.7 (0.2)

The optical coupling layer of Example 1 was also tested and was found tobe less preferred due to increased stiffness in view of comprising alower concentration of polymeric silane surface treatment.

What is claimed is:
 1. A coating composition comprising: at least 40wt.-% inorganic nanoparticles having a refractive index of at least1.85; and a polymeric silane surface treatment having a weight averagemolecular weight ranging from 1000 to 5000 g/mole; wherein the polymericsilane surface treatment is the sole polymeric component of the coatingcomposition; and wherein the coating composition has a refractive indexof at least 1.65 and a peak peel force of at least 50 g/cm.
 2. Thecoating composition of claim 1 wherein the polymeric silane surfacetreatment comprises a random acrylic copolymer comprising at least 50wt.-% of repeat units derived from one or more alkyl (meth)acrylatemonomers comprising 4 to 18 carbon atoms.
 3. The coating composition ofclaim 1 wherein the polymeric silane surface treatment further comprisesa terminal alkoxy silane group.
 4. The coating composition of claim 1wherein the polymeric silane surface treatment has a Tg ranging from−20° C. to −80° C.
 5. The coating composition of claim 1 wherein theinorganic nanoparticles further comprise a non-polymeric surfacetreatment.
 6. The coating composition of claim 5 wherein thenon-polymeric surface treatment has a refractive index of at least 1.50.7. The coating composition of claim 1 wherein the inorganicnanoparticles comprise titania.
 8. The coating composition of claim 1wherein the polymeric silane surface treatment comprises repeat unitscomprising pendant reactive groups selected from hydroxyl groups, acidgroups, or amine groups.
 9. The coating composition of claim 8 whereinthe coating composition comprises a crosslinker that crosslinks thependant reactive groups.
 10. The coating composition of claim 1 whereinthe coating composition is substantially free of (meth)acrylatecomponents having a molecular weight of 1,000 g/mole or less.
 11. Thecoating composition of claim 1 wherein the coating composition issubstantially solvent free.
 12. The coating composition of claim 1wherein the polymeric silane surface treatment comprises a randomacrylic copolymer comprising at least 50 wt.-% of repeat units derivedfrom one or more alkyl (meth)acrylate monomers comprising 4 to 18 carbonatoms.
 13. The coating composition of claim 1 wherein the polymericsilane surface treatment has a Tg ranging from −20° C. to −80° C.